A number of methods for producing N-methyl-N-vinylacetamide have been proposed to date. For example, a method of reacting vinyl acetate and N-methylacetamide in the presence of base such as dimethyl aminopyridine and the like have been disclosed (Patent Document 1: JP-A-H08-59584; U.S. Pat. No. 5,641,881). However, these methods do not disclose a substance inhibiting polymerization of N-methyl-N-vinylacetamide.
On the other hand, a radical scavenger having at least two glycine units has been proposed as a polymerization stabilizer of N-vinylacetamide compounds (Patent Document 2: JP-A-2007-533624; U.S. patent publication No. 2006/287548). However, these scavengers need to be synthesized separately to be added to the compound and furthermore may have an adverse affect such as coloring on the polymer if the scavengers remained in the polymer after polymerization.
Also, a method for producing highly polymerizable N-vinyl carboxylic acid amide (Patent Document 3: JP-A-H08-81428) has been disclosed. However, the invention relates to highly polymerizable N-vinyl carboxylic acid amide, high molecular weight polymer produced thereof and purifying treatment of N-vinyl carboxylic acid amide, and does not disclose polymerization inhibition, stabilization and polymerization control.
N-methyl-N-vinylacetamide is used as an intermediate and a material for industrial chemicals such as surfactant, a reactive diluent, and medicines. Since N-methyl-N-vinylacetamide is liquid at ordinary temperatures, it is at risk for starting polymerization during storage and transportation. Once polymerization occurs, it is impossible to stop it, which may cause a significant accident. But Patent Document 3 does not disclose the stability of the monomer.
N-methyl-N-vinylacetamde homopolymer and copolymer (N-methyl-N-vinylacetamide-based polymer) can be obtained by polymerizing N-methyl-N-vinylacetamide only or by copolymerizing it with other monomers. These polymers can be used for contact lenses, thickners for oil drilling, gas hydrate inhibitors, coating agents, bio-based materials, a base for drug delivery systems, a base for cosmetics, lubricant additives for fuels, a coagulant, a liquid absorbent, a thickner and the like. However, since the polymerizability of material monomers is not the same among the production lots, there has been a problem of difficulty in obtaining polymers having desired physical properties such as molecular weight and concentration of residual monomers.    [Patent Document 1] JP-A-H08-59584    [Patent Document 2] JP-A-2007-533624    [Patent Document 3] JP-A-H08-81428